1. Field of the Invention
The present invention relates to a door curtain anti-dropping device for an electric rolling door, and particularly, to a door curtain anti-dropping device driven by a winding shaft of a rolling door, wherein when a door operator chain is broken such that door curtain drops down with an abnormal speed, the anti-dropping device can lock the winding shaft immediately.
2. Description of the Related Art
For a rolling door, generally, it is quite heavy. Especially, for a large-sized warehouse door, it can reach even up to several tons. Hence, once it drops down vertically out of control, its destruction and lethality is very horrible. Therefore, building code basically has requirements for a rolling door design. That is to say, when a door curtain is moved up or down, the possibility of dangers caused by human factors or non-human factors, shall not happen. According to the inventor's practical experience, the main factors of potential dangers comprise: power outage and broken chain which can make the door curtain drop down by its own weight. As such, a conventional rolling door is installed with a preloading mechanism for balancing partial weight of the door curtain. However, it can be understood that the preloading mechanism only keeps the door curtain balance at the upper end point or the bottom end point. Once the door curtain departs from the upper end point, if it loses control, the door curtain still drops downward under the influence of the gravity.
Many known related documents for preventing the door curtain from dropping down abnormally are proposed. For example, as shown in FIGS. 6 and 6a, which are copied from U.S. Pat. No. 7,686,150 by the present inventor, a safety door speed limiting device comprises an input force shaft (10′), one end of which is driven by a door operator (1′) so as to drive a hollow shaft (20′) and a third shaft (23′) via a first gear (11′) and a second gear (12′) disposed at the other end of the input force shaft (10′), the hollow shaft (20′) receiving and securing one end of a winding shaft (4′) at its center, and the third shaft (23′) connecting to an extension shaft (25′); a braking device (3′), including a drive gear (31′) firmly connected to the extension shaft (25′); a driven shaft (33′), pivoting on a shaft hub (35′), the shaft hub (35′) being firmly connected to the winding shaft (4′) and rotating together with the hollow shaft (20′); an idle gear (37′), located between the drive gear (31′) and the driven gear (33′) to adjust the rotational speeds of the driven gear (33′) and the hollow shaft (20′) to be coincident; a clutch mechanism (39′) with a cam (36′) disposed on the shaft hub (35′), on the circumference of the cam (36′), there being a plurality of protrusions (361′) and recesses (362′), one end of the driven gear (33′) including a plurality of tabs (34′) and a plurality of notches (341′) to surround the cam (36′); and a plurality of rollers (38′), located in the notches (341′) among the tabs (34′) and corresponding to the recesses (362′) of the cam (36′), respectively, wherein the clutch mechanism (39′) further includes a secured limitation part (32′) for limiting the cam (36′), the tabs (34′) and the rollers (38′) to run in a space. Accordingly, in the case of no potential difference between the rollers (38′) and the cam (36′), the driven gear (33′) and the shaft hub (35′) are constrained to run synchronously. When the rotational speed of the winding shaft (4′) has an abnormal change, the dislocation between the rollers (38′) and the cam (36′) is created immediately to lock the shaft hub (35′) and brake the winding shaft (4′).
The above-mentioned patent can lock the winding shaft, when the door curtain drops down abnormally. However, once the winding shaft is locked, it is quite troublesome to unlock the lock state of the winding shaft. It is necessary to dismantle the door operator, and therefore, there is still a room for the mechanism to improve.